The technical field of this invention is signal processing and, in particular, the addition of information to broadcast motion picture or television signals.
Conventionally, television broadcast signals in the United States are transmitted in accordance with the National Television Systems Committee (NTSC) standards. The NTSC code provides a format whereby motion pictures (i.e. sequences of still frames) can be broadcast and reconstructed in a receiver for display in rapid succession to the viewer. There is considerable interest in adding additional information to broadcast signals in manner that would be compatible with the NTSC format and yet permit an advanced receiver to decode the additional information.
A goal of such "extended definition television" (EDTV) systems is the production of a broadcast signal that can be received with negligible loss of quality on existing home equipment but when received on an advanced receiver can produce a picture with improved resolution, aspect ratio, or sound.
However, it is difficult to find channel space within the NTSC signal format for additional data with which to enhance the image quality and sound without at the same time causing deterioration of performance of standard receivers.
Various proposals for EDTV systems have been made including, for example, use of blank regions of the spectrum, higher order interlace, time compression at the edges, and altered modulation techniques. Unfortunately, these systems typically result in visible degradation of the image.
Other proposals include the addition of new subcarriers, which would require substantial modification of the present NTSC format, or the use of a second transmission channel to transmit the additional information.
There exists a need for an extended definition television system which could add information to standard NTSC signals to provide enhanced viewing for a receiver attuned to decode such additional information while also permitting viewing with a standard receiver with minimal visual disturbances. Such an extended definition system would satisfy a long-felt need in the art.